• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.22-27
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• 1995

본 연구로부터 얻어진 결론은 다음과 같다. 1. 본 연구에서는 TBM에 의한 파이롯트 터널의 효율성을 극대화한 이방향 천공 발파공법을 개발, 현장실험을 통하여 그 효용성을 입증하였다. 2. NATM 공법에 의한 발파보다 TBM을 이용하여 파이롯트 터널을 굴착하여 확대발파할 경우 상당한 지반진동 경감효과를 얻을 수 있을 것으로 판단된다. 3. 이방향 천공 발파공법의 현장시험 결과, 측정된 지반 진동치는 20% 이상의 진동 경감효과가 있는 것으로 분석되었다. 4. 기존공법과 신공법의 상대비교를 위한 수치해석 결과, 신공법의 방사상 방향 발파는 기존공법의 종방향 발파에 비하여 관심의 대상이 되는 발파공 직상부에서 진동치가 크게 경감되었다.

• Tunnel and Underground Space
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• v.14 no.6 s.53
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• pp.440-449
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• 2004

Rock mass includes natural discontinuities such as joints and faults during its formation. Discontinuities are also referred as planes of weakness because of their weak mechanical characteristics. In the design of underground structures, it is necessary to consider the properties of discontinuities to insure the stability. During the excavation of a tunnel, these discontinuities have to be identified as early as possible so that proper change in excavation method or support design can be made accordingly. The excavation of the tunnel in a stable rock mass causes a 3-dimensional arching effect around the excavation face. It was revealed by previous studies that the existence of a weak zone or a fault zone ahead of tunnel foe induces a typical displacement tendency of convergence. For better understanding of the meaning of influence/trend lines of various displacement components, three-dimensional numerical analyses were conducted while varying deformation moduli, thicknesses and orientations of discontinuities. Numerical results showed that the changes in influence/trend lines of various displacement components were very similar to those by measurements. The discrepancies from the expected values were dependent on the physical properties, thicknesses and orientations of discontinuities.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.209-218
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• 2005

In a NATM tunnel, fully grouted bolts are widely used as part of supporting system. Grouted bolts play an important role not as to take some parts of load acting on the tunnel lining but as to reinforce the ground adjacent the tunnel. In conjunction with tunnel construction, the presence of groundwater may pose a number of difficulties. With respect to tunnel design, influences of groundwater on tunnel behavior have been considered in many aspects. However, the effect on grouted bolts has been rarely investigated. In this study, the behavior of grouted bolts, which are affected by the seepage forces, was examined. In order to investigate the effects of seepage forces, the theoretical solutions for a drained condition were proposed. Based on the theoretical solutions, ground reaction curves considering seepage forces were obtained. By comparing the ground reaction curves supported by grouted bolts with those for the unsupported cases, the effect of reinforcement was evaluated. Finally, through comparison between supported ground react ion curve s in the drained condition and those in the case of groundwater flow, it was observed that the grout ed bolts are more structurely beneficial when the seepage occurs towards the tunnel than when there is no groundwater flow.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1982-1990
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• 2010

Excepting tunnel of dorimstream - ccachimountain station section, the subway line No.2th section was build using ASSM and NATM methods because of soil pressure and land condition. The way of dealing underground water was selected without sufficient preconsideration of geographical features, ground condition, influence of lowing underground water, and long-term cost of running maintenance so that the form of undrained tunnel was build having decreased construction characteristics and technically improper elements. The form of partial drainage is very difficult to manage structures of tunnel, because water leakage, water pressure causing cracks of lining concretes and scaling are constantly happened. so partial drainage suggest that setting reinforced Anchor Bolt to prevent buoyancy and should increase center drainage way up to height of railroad. Partial drainage suggest that holey pipe(${\phi}$350mm) manhole, drainage checking pipe manhole are should be regularly dredged, when changing roadbed(gravel${\rightarrow}$concrete) drainage checking pipe manhole should be build and setting a limitation of entering underground water's quantities. Beside drainage degree in changed section of structures causing instability of structures is continuous degree. so if efficient drainage way and the patterns of flaws, problems are considered in survey, it will be expected to have a advantage condition in maintenance part.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.411-429
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• 2022

Instrumentations are essential in NATM tunnels, however measuring instruments are installed and applied without performance verification procedures due to insufficient research on methods, procedures, regulations, etc. to verify the reliability of the measuring instruments. In this study, domestic and foreign regulations relating to the verification and calibration of instruments were investigated and necessities for accreditation standards were proposed. In order to identify the causes of the defects, an external inspection was performed on rock bolt stressmeter and rod extensometer, which are measuring instruments with relatively complex structures. For verifying the performance of these instruments, verification devices were developed that can load step-by-step and the causes of defects were identified in measuring instruments of nine domestic manufacturers. Through the performance test, a number of measuring instruments were found to be defective. It was important to test the performance of the instruments in the state of a finished product and accordingly performance inspection methods and procedures were proposed. The results of this study are expected to help preparing related regulations for verifying instrument performance and selecting instruments in the field.

• Tunnel and Underground Space
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• v.33 no.4
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• pp.255-264
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• 2023

As the demand for urban underground space increases recently, urban tunnel planning is actively progressing. In the urban area, a underground station is planned in consideration of the living environment of residents, and 2-arch tunnel is applied for the stability of existing structures and reduction of environmental damage. However, since the depth of weak rock mass is deeply distributed in the urban area due to severe weathering, careful planning is required to secure tunnel stability. In addition, if TBM mechanical excavation is applied as the main tunnel excavation method considering the composite ground in urban area, the construction connectivity with the 2-arch tunnel of the NATM concept may be deteriorated. In this study, the design case of applying TBM pre-excavation type 2-arch tunnel for the first time in Korea was mainly described. The main considerations for the segment design of TBM pre-excavation type 2-arch tunnel were explained for side tunnels. Also, a stability analysis was conducted to verify the effectiveness and adequacy of the TBM pre-excavation type 2-arch tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.4
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• pp.305-330
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• 2023

Unlike NATM tunnels, Shield TBM tunnels have split linings. Therefore, the stress distribution of the lining is different even if the lining is under the same load. Representative methods for analyzing the stress generated in lining in Shield TBM tunnels include Non-joint Mode that does not consider connections and a 2-ring beam-spring model that considers ring-to-ring joints and segment connections. This study is an analysis method by Break-joint Mode. However, we do not consider the structural role of segment lining connections. The effectiveness of the modeling is verified by analyzing behavioral characteristics against vibration loads by modeling with segment connection interfaces to which vertical stiffness and shear stiffness, which are friction components, are applied. Unlike the Non-joint mode, where the greatest stress occurs on the crown for static loads such as earth pressure, the stress distribution caused by contact between segment lining and friction stiffness produced the smallest stress in the crown key segment where segment connections were concentrated. The stress distribution was clearly distinguished based on segment connections. The results of static analysis by earth pressure, etc., produced up to seven times the stress generated in Non-joint mode compared to the stress generated by Break-joint Mode. This result is consistent with the stress distribution pattern of the 2-ring beam-spring model. However, as for the stress value for the train vibration load, the stress of Break-joint Mode was greater than that of Non-joint mode. This is a different result from the static mechanics concept that a segment ring consisting of a combination of short members is integrated in the circumferential direction, resulting in a smaller stress than Non-joint mode with a relatively longer member length.

• Journal of Korean Society of Steel Construction
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• v.24 no.3
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• pp.267-278
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• 2012

In general, the H-shaped steel ribs or triangular lattice girders have been mostly used in constructing tunnels through the NATM construction method. The H-shaped steel rib has higher flexural and axial strength than the triangular lattice girder, but many unexpected gaps can occur in the concrete lining system after shotcreting if the H-shaped steel rib is used as the support system. To achieve better shotcreting quality, the triangular lattice girder was developed. However, in general, the triangle lattice girder has low flexural and axial strength. Likewise, the triangular lattice girder, which has circular sectional members, has so many fractures from welded points at the joints between the members. Finally, the new type of tetragonal lattice girder was developed to overcome those problems. In this study, the structural performance of the tetragonal lattice girders was evaluated through analytical and experimental studies. In the analytical studies, the four-point bending analysis, the traditional evaluation method to determine the flexural strength of the lattice girder, was performed. Moreover, the linear-elastic analysis and stability analysis of the arch structure made by the lattice girders were performed to measure structural performance. Experiments were likewise performed to compare the structural performances of the tetragonal girder with traditional triangular lattice girders.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.249-257
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• 2006

The spatial distribution of design parameters greatly affects tunnel behavior during and after construction, as well as in the long-term temporal responses. However, the tunnel design parameters commonly used in numerical modeling tend to be representative or average values of global-scale properties. Furthermore, the uncertainty and spatial variation of the design parameters increase as the tunnel scale increases. Consequently, the probability of failure also increases. In order to achieve structural stability in large-section tunnels, the design framework must take into consideration the quantitative effect of design parameter variations on tunnel behavior. Therefore, this paper suggests a statistical approach to numerical modeling to explore the effect of spatially distributed design parameters in a circular tunnel. Also, the effect of spatial variation in the lining strength is studied in this paper. The numerical results suggest that the deformation around the tunnel increases with an increase in the variation of the design parameters.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.483-494
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• 2022

Owing to the saturation of ground spaces in downtown areas, underground spaces are being developed increasingly. Underground spaces are utilized for transportation, water supply and sewerage, communication zones, electric power zones, and various cultural complexes. In Korea, for excavating underground spaces, blasting methods using gunpowder such as the New Austrian Tunneling Method (NATM) are mainly used. However, the blasting method causes vibration and noise during tunnel excavation, generating many complaints from residents in the vicinity of the excavation site. To address this problem, various methods have been developed, and recently, vibration and noise have been reduced using deep excavation. This study predicts blast vibration changes according to the depth, under the same blasting and tunnel conditions, using numerical analysis based on the blast vibration measurement data of the GTX-A route, the tunnel cross-section drawings, and ground investigation reports. Furthermore, the necessary separation distance from densely populated areas such as residential areas is suggested by analyzing the trend of decreasing blast vibration according to the distance from ground surface directly above the blasting location.